Note that every GUI component created is a child of the window, this is done by specifying the parent element (wdwLogin, in this case) when creating the component.

This is very useful because not only does it mean that all the components are attached to the window and will move with it, but also that any changes done to the parent window will be applied down the tree to these child components. For example, we can now hide all of the GUI we just created by simply hiding the window:

guiSetVisible(wdwLogin, false) --hides all the GUI we made so we can show them to the player at the appropriate moment.

Using the function we wrote

The createLoginWindow function is now complete, but it won't do anything until we call it. It is recommended to create all GUI when the client resource starts, hide them, and show them to the player later when needed. Therefore, we'll write an event handler for "onClientResourceStart" to create the window:

-- attach the event handler to the root element of the resource
-- this means it will only trigger when its own resource is started
addEventHandler("onClientResourceStart", getResourceRootElement(getThisResource()),
function ()
createLoginWindow()
end
)

As this is a log in window, we now need to show the window when the player joins the game.
This can be done using the same event, "onClientResourceStart", so we can modify the above code to include showing the window:

Note that we are now writing more code for our existing 'onClientResourceStart' handler. This is not a new event handler and is meant to replace what you already have.

addEventHandler("onClientResourceStart", getResourceRootElement(getThisResource()),
function ()
-- create the log in window and its components
createLoginWindow()
-- output a brief welcome message to the player
outputChatBox("Welcome to My MTA:SA Server, please log in.")
-- if the GUI was successfully created, then show the GUI to the player
if (wdwLogin ~= nil) then
guiSetVisible(wdwLogin, true)
else
-- if the GUI hasnt been properly created, tell the player
outputChatBox("An unexpected error has occurred and the log in GUI has not been created.")
end
-- enable the players cursor (so they can select and click on the components)
showCursor(true)
-- set the input focus onto the GUI, allowing players (for example) to press 'T' without the chatbox opening
guiSetInputEnabled(true)
end
)

Note that we have a simple security check before making the window visible, so in the unlikely event that the window has not been created, meaning wdwLogin is not a valid element, we don't get an error and just inform the player what has happened.
In the next step, we will create the button functionality for the log in button.

Scripting the button

Now that we have created our GUI and shown it to the player, we need to make it work.

Detecting the click

When the player clicks on any part of the GUI, the event "onClientGUIClick" will be triggered for the GUI component you clicked on. This allows us to easily detect any clicks on the GUI elements we want to use.
For example, we can attach the event to the btnLogin button to catch any clicks on it:

-- attach the event onClientGUIClick to btnLogin and set it to trigger the 'clientSubmitLogin' function
addEventHandler("onClientGUIClick", btnLogin, clientSubmitLogin, false)

Note the final argument passed is "false". This indicates that the event will only trigger directly on btnLogin, not if the event has propagated up or down the tree. Setting this to "true" while attaching to gui elements will mean that clicking on any element in the same branch will trigger this event.

This line of code can now be added inside the createLoginWindow function. It is a common mistake to try and attach events to non-existant GUI elements, so make sure you always attach your events after the gui element (in this case, the button) has been created:

Note that we are now writing more code for our existing 'createLoginWindow' function.

Managing the click

Now that we can detect when the player clicks on the button, we need to write code to manage what happens when they do.
In our onClientGUIClick event handle, we told it to call the function clientSubmitLogin whenever btnLogin is clicked.
Therefore, we can now use the function clientSubmitLogin to control what happens when the button is clicked:

-- create the function and define the 'button' and 'state' parameters
-- (these are passed automatically by onClientGUIClick)
function clientSubmitLogin(button,state)
-- if our login button was clicked with the left mouse button, and the state of the mouse button is up
if button == "left" and state == "up" then
-- move the input focus back onto the game (allowing players to move around, open the chatbox, etc)
guiSetInputEnabled(false)
-- hide the window and all the components
guiSetVisible(wdwLogin, false)
-- hide the mouse cursor
showCursor(false)
end
end

Now, when the button is clicked, the window will be hidden and all controls will be returned to the player. Next, we will tell the server to allow the player to spawn.

Triggering the server

Triggering the server can be done using triggerServerEvent. This allows you to trigger a specified event on the server from the client. The same can be done in reverse using triggerClientEvent.
Here, we use the triggerServerEvent function to call our own custom event on the server, named "submitLogin", which will then control the spawning of the player serverside.

Note that we are now writing more code for our existing 'clientSubmitLogin' function. This is not a new function and is meant to replace what you already have.

function clientSubmitLogin(button,state)
if button == "left" and state == "up" then
-- get the text entered in the 'username' field
local username = guiGetText(edtUser)
-- get the text entered in the 'password' field
local password = guiGetText(edtPass)
-- if the username and password both exist
if username and password then
-- trigger the server event 'submitLogin' and pass the username and password to it
triggerServerEvent("submitLogin", getRootElement(), username, password)
-- hide the gui, hide the cursor and return control to the player
guiSetInputEnabled(false)
guiSetVisible(wdwLogin, false)
showCursor(false)
else
-- otherwise, output a message to the player, do not trigger the server
-- and do not hide the gui
outputChatBox("Please enter a username and password.")
end
end
end

Creating the serverside event

At this point we now have all the code needed on the client side, so open up your serverside 'script.lua' file (from the Introduction to Scripting) or another suitable serverside file to work with.

On the server side, recall that we are spawning the player as soon as they login.
So, first of all, we will need to define the custom event that we used before on the client. This can be done using addEvent and addEventHandler.

-- create our loginHandler function, with username and password parameters (passed from the client gui)
function loginHandler(username,password)
end
-- define our custom event, and allow it to be triggered from the client ('true')
addEvent("submitLogin",true)
-- add an event handler so that when submitLogin is triggered, the function loginHandler is called
addEventHandler("submitLogin",root,loginHandler)

Logging in

Now we have a function that is called through the custom event 'submitLogin', we can start to work on logging in and spawning the player, using our 'loginHandler' function:

function loginHandler(username,password)
-- check that the username and password are correct
if username == "user" and password == "apple" then
-- the player has successfully logged in, so spawn them
if (client) then
spawnPlayer(client, 1959.55, -1714.46, 10)
fadeCamera(client, true)
setCameraTarget(client, client)
outputChatBox("Welcome to My Server.", client)
end
else
-- if the username or password are not correct, output a message to the player
outputChatBox("Invalid username and password. Please re-connect and try again.",client)
end
end
addEvent("submitLogin",true)
addEventHandler("submitLogin",root,loginHandler)

For the purposes of this tutorial, a very basic username and password system is shown. For a more comprehensive alternative, you can use the Account System or a MySQL database.

Also note the use of the variable "client", it's an internal variable used by MTA to identify the player who triggered the event.

Finally, do not forget to include the new gui.lua file in the meta.xml of the main resource, and label it as a client script:

<script src="client/gui.lua" type="client" />

At this point, we now have a basic login window that checks the player's username and password when the login button is clicked. If they are correct, the player is automatically spawned.